Generally, a structure of a lamp comprises an optical cover, a tubular housing, a cap, and a light source module and a driving module mounted inside the tubular housing, in which the optical cover is a transparent or translucent optical element for transmitting light, the cap is used for connecting to electrical power, the light source module comprises LED or other types of light source, and the driving module is used for supplying power to the light source module. Usually, for the purpose of water resistance, the lamp is designed to be totally enclosed, i.e., an upper end of the tubular housing being connected to the optical cover hermetically, a lower end of the tubular housing being connected to the cap hermetically. The heat generated by the light source module and the driving module when in operation will make the gas inside the lamp expand, while the gas inside the lamp will contract when the lamp is turned off or the surrounding temperature decreases. When the gas inside the lamp causes the internal pressure to change due to expanding with heat and contracting with cold, the hermetically connected portions of the lamp are easy to be damaged. Once the hermetically connected portions of the lamp are damaged, the lamp will lose its capability of waterproof, which will cause a severe safety risk.